Thin Film Comprising Titanium Oxide, and Method of Producing Thin Film Comprising Titanium Oxide

ABSTRACT

A thin film is provided that primarily comprises titanium oxide and includes Ti, Ag and O. The thin film contains 29.6 at % or more and 34.0 at % or less of Ti, 0.003 at % or more and 7.4 at % or less of Ag, and oxygen as the remainder thereof and has a ratio of oxygen to metals, O/(2Ti+0.5Ag), of 0.97 or more. The thin film has a high refractive index and a low extinction coefficient. In addition, the thin film has superior transmittance, minimally deteriorates in reflectance, and is useful as an interference film or a protective film for an optical information recording medium. The film may also be applied to a glass substrate to provide a heat reflective film, an antireflective film, or an interference filter. A method of producing the thin film is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. application Ser. No.12/808,469 which is the National Stage of International Application No.PCT/JP2008/072295, filed Dec. 9, 2008, which claims the benefit under 35USC 119 of Japanese Application No. 2007-326485, filed Dec. 18, 2007,and Japanese Application No. 2008-239951, filed Sep. 18, 2008.

BACKGROUND

The present invention relates to a thin film mainly comprising titaniumoxide having a high refractive index and a low extinction coefficient, asintered sputtering target mainly comprising titanium oxide suitable forproducing the thin film, and a method of producing a thin film mainlycomprising titanium oxide.

In recent years, technology of high-density optical recording disks suchas high-density optical information recording media capable of rewritingwithout requiring a magnetic head has been developed, and these disksare rapidly being commercialized. In particular, CD-RW appeared for thefirst time in 1977 as a rewritable CD, and is the most popularphase-change optical disk today. This CD-RW has a rewrite cycle ofapproximately 1000 times. Further, DVD-RW for use as a DVD has beendeveloped and commercialized, and the layer structure of this disk isidentical with or similar to the structure of CD-RW. This DVD-RW has arewrite cycle of approximately 1000 to 10000 times. These disks record,replay and rewrite information by irradiating an optical beam to causean optical change of the recording material such as its transmittance orreflectance, and are electronic parts that have spread rapidly.

Generally speaking, a phase-change optical disc used as a CD-RW or aDVD-RW has a four-layer structure wherein both sides of a recording thinfilm layer of Ag—In—Sb—Te system or Ge—Sb—Te system or the like aresandwiched between the protective layers of high-melting dielectricssuch as ZnS.SiO₂ or the like, and a silver or silver alloy or aluminumalloy reflective film is additionally provided thereto. Further, inorder to increase the rewrite cycle, an interface layer is providedbetween a memory layer and a protective layer as necessary. Thereflective layer and the protective layer are demanded to have anoptical function capable of increasing the reflectance differencebetween the amorphous portion and the crystal portion of the recordinglayer, and also demanded to have a function of protecting the recordingthin film from moisture and heat deformation as well as a function forcontrolling the thermal conditions upon recording (see “Kogaku”magazine, volume 26, no. 1, pages 9 to 15).

In recent years, in order to enable high-capacity and high-densitystorage, an optical recording medium of single-sided double (dual) layerhas been proposed (see Publication of Unexamined Japanese ApplicationNo. 2006-79710). Japanese Application Publication No. 2006-79710 has afirst information layer formed on a substrate 1 and a second informationlayer formed on a substrate 2 from the incident direction of the laserbeam, and these information films are laminated so as to face each othervia an interlayer. In the foregoing case, the first information layer isconfigured from a recording layer and a first metal reflective layer,and the second information layer is configured from a first protectivelayer, a second protective layer, a recording layer and a second metalreflective layer. In addition, a hard coating layer for protecting thedisk from scratches and contamination or the like, a thermal diffusionlayer, and other layers may also be arbitrarily formed. In addition,various types of materials have been proposed for the foregoingprotective layer, recording layer, reflective layer, and other layers.

The protective layer of high-melting dielectrics must be durable againstrepeated thermal stress caused by the heating and cooling and must notallow such thermal effect to influence the reflective film or otherareas, and it is also required to be thin and have low reflectivity andstrength to prevent alteration. From this perspective, the dielectricprotective layer plays an important role. In addition, needless to say,the recording layer, the reflective layer, the interference film layerand the like are also important from the perspective of enabling theelectronic parts such as CDs and DVDs to fulfill their functionsrespectively.

The respective thin films of a multilayer structure are usually formedwith the sputtering method. This sputtering method is to make a positiveelectrode substrate and a negative electrode target face each other, andgenerates an electric field by applying a high voltage between thesubstrate and the target under an inert gas atmosphere. The sputteringmethod employs a principle where plasma is formed by the collision ofionized electrons and the inert gas at the stage of generating anelectric field, the positive ions in this plasma collide with the target(negative electrode) surface to knock out the constituent atoms of thetarget, and the extruded atoms adhere to the opposing substrate surfaceto form a film.

Under the foregoing circumstances, a target using titanium oxide(TiO_(x)) is being proposed as a sputtering target for forming a heatreflective film and an antireflective film (see Japanese Patent No.3836163). In the foregoing case, Japanese Patent No. 3836163 describesthat the specific resistance value is set at 0.35 Ωcm or less in orderto stabilize the discharge during the sputtering, and DC sputteringbecomes possible, whereby a film of high refractive index can beobtained. Nevertheless, since the film transmittance will deteriorate,measures of setting the oxygen content to be 35 wt % or more andadditionally introducing oxygen are being adopted. Moreover, since thedeposition rate will deteriorate due to the introduction of oxygen,metal oxide is added in order to improve the deposition rate. However,there are problems in its application as precision optics or electronicparts requiring films having a high refractive index and low absorption.In particular, it is considered that there are problems on the shortwavelength side in the vicinity of 400 nm.

SUMMARY

In light of the foregoing problems, it is an object of this invention toprovide a thin film mainly comprising titanium oxide having a highrefractive index and a low extinction coefficient, a sintered sputteringtarget mainly comprising titanium oxide suitable for producing the thinfilm, and a method of producing a thin film mainly comprising titaniumoxide. Another object of this invention is to obtain a thin film thathas superior transmittance, minimally deteriorates in reflectance, andis useful as an interference film or a protective film for an opticalinformation recording medium. It is also possible to apply this thinfilm to a glass substrate; that is, which can be used as a heatreflective film, an antireflective film, and an interference filter.

In order to achieve the foregoing objects, as a result of intense study,the present inventors discovered that it is extremely effective to addsilver or silver oxide to titanium oxide in order to obtain a materialthat maintains transmittance and prevents the deterioration inreflectance without losing its properties as an interference film or aprotective film for an optical information recording medium.

Based on the foregoing discovery, the present invention provides a thinfilm mainly comprising titanium oxide, wherein the thin film comprisescomponents of Ti, Ag and O and contains 29.6 at % or more and 34.0 at %or less of Ti, 0.003 at % or more and 7.4 at % or less of Ag, and oxygenas the remainder thereof, and O/(2Ti+0.5Ag) as a ratio of oxygen tometals is 0.97 or more. The thin film mainly comprising titanium oxidemay have an O/Ti ratio of oxygen to Ti of 2 or more and may have arefractive index in a wavelength region from 400 to 410 nm of 2.60 ormore. The thin film mainly comprising titanium oxide may have anextinction coefficient in a wavelength region from 400 to 410 nm of 0.1or less, or 0.03 or less. The thin film may be used as an interferencefilm, a protective film, or an optical recording medium.

In addition, the present invention may provide a sintered sputteringtarget suitable for producing a thin film mainly comprising titaniumoxide, wherein the target comprises components of Ti, Ag and O, containsthe respective components at a composition ratio of(TiO_(2-m))_(1-n)Ag_(n) (where: 0≦m≦0.5, and 0.0001≦n≦0.2), and has aspecific resistance of 10 Ωcm or less. Alternatively, “n” may beprovided as: 0.01≦n≦0.2. The sintered sputtering target may have anaverage grain size of Ag phase existing in the sintered sputteringtarget of 15 μm or less.

A method of producing a thin film mainly comprising titanium oxide mayinclude using a sintered sputtering target, which comprises componentsof Ti, Ag and O, contains the respective components at a compositionratio of (TiO_(2-m))_(1-n)Ag_(n) (provided 0≦m≦0.5, and 0.0001≦n≦0.2),and has a specific resistance of 10 Ωcm or less, to perform sputteringunder an argon gas atmosphere without oxygen or with 0.1 to 16% ofoxygen, whereby formed on a substrate is a thin film which contains 29.6at % or more and 34.0 at % or less of Ti, 0.003 at % or more and 7.4 at% or less of Ag, and oxygen as the remainder thereof, and in whichO/(2Ti+0.5Ag) as a ratio of oxygen to metals is 0.97 or more. Themethod, when deposition is performed by way of DC sputtering and anoxygen gas ratio in the sputtering atmosphere is represented in b (%),may be performed with an oxygen gas ratio adjusted to be in a range of0≦b≦83.3n-0.17 when the composition ratio n of Ag in the sputteringtarget is 0.0001≦n≦0.01, and an oxygen gas ratio adjusted to be in arange of 17n-0.17≦b≦83.3n-0.17 when the composition ratio n of Ag is0.01≦n≦0.2. The method of producing a thin film mainly comprisingtitanium oxide may include sputtering in which the oxygen gas ratio b isequal to 0% when the composition ratio m is in a range of 0≦m≦0.05 andthe composition ratio n of Ag is 0.0001≦n≦0.01.

As described above, the present invention provides a thin film mainlycomprising titanium oxide having a high refractive index and a lowextinction coefficient, a sintered sputtering target mainly comprisingtitanium oxide suitable for producing the thin film, and a method ofproducing a thin film mainly comprising titanium oxide. The thin filmobtained by the present invention yields a great effect as films andlayers for an optical information recording medium. In addition, thethin film of the present invention has superior transmittance, minimallydeteriorates in reflectance, and is particularly useful as aninterference film or a protective film for an optical informationrecording medium. The protective layer of high-melting dielectrics mustbe durable against repeated thermal stress caused by the heating andcooling, and must not allow such thermal effect to influence thereflective film or other areas, and it is also required to be thin andhave low reflectivity and strength to prevent alteration. The thin filmmainly comprising titanium oxide of the present invention has propertiesthat can be applied to such a material. In addition, since the oxygencontent during sputtering can be adjusted to be within a low range, thepresent invention also yields an effect of being able to inhibitdeterioration of deposition rate.

DETAILED DESCRIPTION

The thin film mainly comprising titanium oxide of the present inventioncomprises, as described above, components of Ti, Ag and O, contains 29.6at % or more and 34.0 at % or less of Ti, 0.003 at % or more and 7.4 at% or less of Ag, and oxygen as the remainder thereof, and has acomposition ratio in which O/(2Ti+0.5Ag) as a ratio of oxygen to metalsis 0.97 or more. The existence of Ag yields an effect of increasing therefractive index of the thin film. If the amount of Ag is less than0.003, the effect of adding Ag is small, and if the amount of Ag exceeds7.4, the extinction coefficient of the thin film in a wavelength regionfrom 400 to 410 nm tends to increase. Thus, it is preferable that theabundance of Ag in the thin film is 0.03 at % or more and 7.4 at % orless.

Although the reason why the refractive index increases is notnecessarily clear, it is considered to be because silver (Ag) isdispersed as fine particles (nanoparticles and the like) in theamorphous film of titanium oxide. In certain cases, silver may partiallyexist as silver oxide (Ag₂O, Ag₂O₂ or the like), but such partialexistence as silver oxide does not cause any particular problem, and theimprovement in the refractive index is similarly acknowledged. Theexistence of silver oxide can be confirmed when the peak position ofAg3d is 368.0 eV or less in the XPS analysis. The material having a highrefractive index obtained as described above will become a morefavorable material since the possibility of optical multilayer filmdesign can be expanded.

The foregoing thin film is an amorphous film, and it is possible toobtain a film in which a refractive index in a wavelength region from400 to 410 nm is 2.60 or more. It is further possible to obtain a thinfilm in which an extinction coefficient in a wavelength region from 400to 410 nm is 0.1 or less, and even 0.03 or less. The foregoingwavelength region from 400 to 410 nm is the wavelength region of a bluelaser. As described above, the refractive index is 2.60 or more in theforegoing wavelength region, and higher the refractive index, the morefavorable it is. Moreover, an extinction coefficient of 0.1 or less, andeven 0.03 or less can be achieved, and lower the extinction coefficient,the more suitable it is for multilayering. This thin film mainlycomprising titanium oxide is effective as an interference film or aprotective film, and particularly useful as an optical recording medium.

The foregoing thin film can be produced by using a sintered sputteringtarget having a composition ratio of (TiO_(2-m))_(1-n)Ag_(n) (provided0≦m≦0.5, and 0.0001≦n≦0.2), and a specific resistance of 10 Ωcm or less.When sputtering is performed in the foregoing case, deposition ispreferably performed in an oxygen-containing atmosphere if the Agcontent is particularly high. Thus, the oxygen in the sputtered filmwill increase. In particular, it is possible to obtain a thin filmmainly comprising titanium oxide having a low extinction coefficient ina wavelength region from 400 to 410 nm by adjusting O/Ti as the ratio ofoxygen to Ti to be 2 or more. The sintered target of the presentinvention has a similar component composition as the thin film, but isnot the same. Specifically, whereas the basic components of the targetinclude Ti, Ag and O, the composition ratio of the respective componentsis (TiO_(2-m))_(1-n)Ag_(n) (provided 0≦m≦0.5, and 0.0001≦n≦0.2). Inaddition, the target has a specific resistance of 10 Ωcm or less.

In the foregoing case, if m exceeds 0.5, the extinction coefficienttends to increase since the oxygen defect becomes too large, andtherefore, m is preferably set to 0.5 or less. In addition, if n is lessthan 0.0001, the effect of adding Ag is small, and if n exceeds 0.2, theextinction coefficient in the case of performing the foregoingdeposition tends to increase. Thus, n is preferably set to 0.0001 ormore and 0.2 or less. Conductivity of the target is required forincreasing the sputtering efficiency, and the target of the presentinvention has such a condition and can be subject to DC sputtering.

Incidentally, as described later, if the composition ratio m is in therange of 0≦m≦0.05 and the composition ratio n of Ag is 0.0001≦n≦0.01,the deposition rate can be considerably adjusted based on the sputteringconditions; that is, based on whether the sputtering atmosphere is to beAr+O₂ gas or only Ar gas. If the composition ratio is 0.05≦m≦0.5 or0.01≦n≦0.2, since the extinction coefficient will increase when thesputtering atmosphere is only Ar gas, it is desirable to use Ar+O₂ gas.In the foregoing case, the target composition will be changed accordingto the purpose of production.

In addition, if the average grain size of the Ag phase existing in thesintered sputtering target is 15 μm or less, DC sputtering can beperformed even more easily. Meanwhile, if the average grain size of theAg phase exceeds 15 μm, abnormal discharge will occur frequently. Thus,the average grain size of the Ag phase is preferably 15 μm or less. Thissintered sputtering target is used to perform sputtering under an argongas atmosphere without oxygen or with 0.1 to 16% of oxygen, whereby atitanium oxide thin film containing Ag and/or Ag oxide can be formed ona substrate.

Upon producing the thin film, as described above, a sintered sputteringtarget, which comprises Ti, Ag and O, contains the respective componentsat a composition ratio of (TiO_(2-m))_(1-n)Ag_(n) (provided 0≦m 0.5, and0.0001≦n≦0.2), and has a specific resistance of 10 Ωcm or less, is usedto perform sputtering under an argon gas atmosphere without oxygen orwith 0.1 to 16% of oxygen. Specifically, it is thereby possible to form,on a substrate, a thin film which comprises 29.6 at % or more and 34.0at % or less of Ti, 0.003 at % or more and 7.4 at % or less of Ag, andoxygen as the remainder thereof, and in which O/(2Ti+0.5Ag) as a ratioof oxygen to metals is 0.97 or more.

In the foregoing case, the preferred conditions in producing the thinfilm mainly comprising titanium oxide of the present invention are that,if deposition is performed by way of DC sputtering and an oxygen gasratio in the sputtering atmosphere is represented in b (%), the oxygengas ratio is adjusted to be in a range of 0≦b≦83.3n-0.17 when thecomposition ratio n of Ag in the sputtering target is 0.0001≦n≦0.01, andthe oxygen gas ratio is adjusted to be in a range of17n-0.17≦b≦83.3n-0.17 when the composition ratio n of Ag is 0.01≦n≦0.2.Nevertheless, as described above, if the composition ratio m is in therange of 0≦m≦0.05 and the composition ratio n of Ag is 0.0001≦n≦0.01,sputtering can also be performed by adjusting the oxygen gas ratio b tobe b=0%. Specifically, it is possible to perform sputtering capable ofsatisfying the optical properties even without any oxygen leakage, andan effect is yielded in that the deposition rate can be considerablyimproved.

In order to produce the target, as the raw materials, high-purity(normally, 4N or higher) titanium oxide (TiO₂) having an average grainsize of 10 μm or less and high-purity (normally, 3N or higher) silverpowder having an average grain size of 20 μm or less are used. These areblended to achieve the composition ratio of the present invention.Subsequently, after blending the foregoing raw materials, they are mixedwith a wet ball mill or a dry blender (mixer) so that the silver will beuniformly dispersed in the titanium oxide powder. After the mixing, themixed powder is filled in a carbon die and subject to hot press. The hotpress conditions may be changed according to the amount of the sinteringmaterial, but hot press is usually performed within the range of 800 to1000° C. and bearing surface pressure of 100 to 500 kgf/cm².Nevertheless, these conditions are merely representative conditions andcan be selected arbitrarily, and there is no particular limitation ofsuch conditions. After the sintering, the sintered compact is machinedinto a target shape. Consequently, it is possible to obtain a target inwhich the basic components thereof are Ti, Ag and O, the respectivecomponents are contained at a composition ratio of(TiO_(2-m))_(1-n)Ag_(n) (provided 0≦m≦0.5, and 0.0001≦n≦0.2), and silver(Ag) and/or silver oxide (Ag₂O, Ag₂O₂ or the like) is dispersed as fineparticles in the matrix of titanium oxide.

EXAMPLES

The present invention is now explained in detail with reference to theExamples and Comparative Examples. Incidentally, these Examples aremerely illustrative, and the present invention shall in no way belimited thereby. In other words, the present invention shall only belimited by the scope of claim for a patent, and shall include thevarious modifications other than the Examples of this invention.

Example 1

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 15 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=99:1 (at %) and mixed. 1 kg ofthe mixed powder was mixed with a wet ball mill so that the silver isuniformly dispersed in the titanium oxide powder. Subsequently, themixed powder that was dried until moisture evaporated was filled in acarbon die and subject to hot press. The hot press conditions were 900°C. and bearing surface pressure of 300 kgf/cm². The obtained sinteredcompact was machined to prepare a target of diameter (φ) 152 mm and 5 mmthickness (t). Consequently, a target having a density of 96% and aspecific resistance of 7 Ωcm was obtained. The grain size of the Agphase in the target was 15 μm. No abnormal discharge occurred during thesputtering. The results are shown in Table 1.

TABLE 1 Grain Size Abnormal Specific of Ag Discharge Target CompositionResistance Sputtering Phase during DC (at %) (Ωcm) Atmosphere (μm)Sputtering Example 1 TiO₂:Ag = 99:1 7 Ar-0.5% O₂ 15 None Example 2TiO₂:Ag = 90:10 2 Ar-2% O₂ 10 None Comparative TiO₂:Ag = 90:10 2 Ar 10None Example 1 Comparative TiO₂ = 100% >100 Ar-2% O₂ — Occurred Example2 Example 3 TiO₂:Ag = 99.9:0.1 10 Ar 10 None Example 4 TiO₂:Ag = 98:2 6Ar-1% O₂ 15 None Comparative TiO₂:Ag = 60:40 0.0003 Ar-10% O₂ 20 NoneExample 3 Example 5 TiO₂:Ag = 90:10 0.5 Ar-2% O₂ 5 None Example 6TiO₂:Ag = 90:10 0.6 Ar-2% O₂ 1 None Comparative TiO₂:Ag = 90:10 15 Ar-2%O₂ 50 Occurred Example 4 Comparative TiO₂:Ag = 90:10 2 Ar-20% O₂ 10 NoneExample 5 Example 7 TiO₂:Ag = 99:1 7 Ar 15 None Example 8 TiO₂:Ag =99.5:0.5 9 Ar 10 None Example 9 TiO₂:Ag = 99.95:0.05 10 Ar 1.5 NoneExample 10 TiO₂:Ag = 99:99:0.01 10 Ar 1.5 None Example 11 TiO_(1.9):Ag =99.95:0.05 0.01 Ar-4% O₂ 1.5 None Example 12 TiO_(1.5):Ag = 99.99:0.010.008 Ar-4% O₂ 1.5 None Example 13 TiO_(1.95):Ag = 99.9:0.1 0.08 Ar 5None Comparative TiO_(1.9):Ag = 99.95:0.05 0.01 Ar 1.5 None Example 6Comparative TiO_(1.5):Ag = 99.99:0.01 0.008 Ar 1.5 None Example 7

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas-0.5% O₂ gasatmosphere with a gas pressure of 0.5 Pa, a gas flow rate of 50 sccm,and a sputtering power of 500 to 1000 w. It was possible to perform DCsputtering without any problem, and it was confirmed that the target hasconductivity. A sputtered film of 500 Å was formed on the glasssubstrate. The film composition analyzed with EPMA was Ti: 32.9 at %,Ag: 0.7 at %, O: 66.4 at %, O/Ti: 2.02, and O/(2Ti+0.5Ag): 1.00. Therefractive index and extinction coefficient of the sputtered film weremeasured. The refractive index and extinction coefficient were measuredwith an ellipsometer using a light wavelength of 405 nm. These resultsare also shown in Table 2. Incidentally, the oxygen level in Table 2 isthe balance. Consequently, the refractive index increased to 2.63, andthe extinction coefficient considerably decreased to 0.005. Thus, it waspossible to form a favorable interference film or protective film for anoptical recording medium.

TABLE 2 Film Composition Deposition Ti Ag O O Rate Refractive Extinction(at %) (at %) (at %) O/Ti (2Ti + 0.5Ag) (Å/sec/kW) Index CoefficientExample 1 32.9 0.7 66.4 2.02 1.00 1.4 2.63 0.005 Example 2 31.2 3.5 65.32.09 1.02 1.1 2.73 0.008 Comparative 32.3 3.7 64 1.98 0.96 1.9 2.65 0.23Example 1 Comparative 33.2 0 66.8 2.01 1.01 0.9 2.59 0.004 Example 2Example 3 33.3 0.04 66.66 2.00 1.00 1.7 2.63 0.01 Example 4 32.3 1.466.4 2.06 1.02 1.4 2.67 0.006 Comparative 26.3 17.5 56.2 2.14 0.92 0.82.5  0.15 Example 3 Example 5 31.0 3.6 65.4 2.11 1.03 1.1 2.72 0.008Example 6 31.4 3.5 65.1 2.07 1.01 1.1 2.74 0.007 Comparative — — — — —1.1 — — Example 4 Comparative 30.7 3.1 66.2 2.16 1.05 0.3 2.59 0.005Example 5 Example 7 33.1 0.7 66.2 2.00 0.99 1.8 2.67 0.02 Example 8 33.30.2 66.5 2.00 1.00 1.8 2.66 0.01 Example 9 33.3 0.02 66.68 2.00 1.00 1.62.62 0.007 Example 10 33.3 0.005 66.695 2.00 1.00 1.6 2.61 0.005 Example11 33.4 0.02 66.58 1.99 1.00 0.7 2.61 0.007 Example 12 33.4 0.006 66.5941.99 1.00 0.6 2.60 0.01 Example 13 33.8 0.04 66.16 1.96 0.98 1.6 2.630.09 Comparative 34.3 0.02 65.68 1.91 0.96 1.6 2.58 0.21 Example 6Comparative 39.9 0.006 60.094 1.51 0.75 1.5 2.54 0.34 Example 7

Example 2

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 10 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=90:10 (at %) and mixed. 1 kgof the mixed powder was mixed with a dry blender so that the silver isuniformly dispersed in the titanium oxide powder. Subsequently, themixed powder was filled in a carbon die and subject to hot press. Thehot press conditions were 920° C. and bearing surface pressure of 350kgf/cm². The obtained sintered compact was machined to prepare a targetof φ 152 mm and 5 mmt. Consequently, a target having a density of 96%and a specific resistance of 2 Ωcm was obtained. The grain size of theAg phase in the target was 10 μm. No abnormal discharge occurred duringthe sputtering. The results are also shown in Table 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas-2% O₂ gasatmosphere with a gas pressure of 0.5 Pa, a gas flow rate of 50 sccm,and a sputtering power of 500 to 1000 w. It was possible to perform DCsputtering without any problem, and it was confirmed that the target hasconductivity. A sputtered film of 500 Å was formed on the glasssubstrate. The film composition was Ti: 31.2 at %, Ag: 3.5 at %, O: 65.3at %, O/Ti: 2.09, and O/(2Ti+0.5Ag): 1.02. The refractive index andextinction coefficient of the sputtered film were measured. Therefractive index and extinction coefficient were measured with anellipsometer using a light wavelength of 405 nm. These results are alsoshown in Table 2. Consequently, the refractive index increased to 2.73,and the extinction coefficient considerably decreased to 0.008. Thus, itwas possible to form a favorable interference film or protective filmfor an optical recording medium.

Comparative Example 1

In this Comparative Example, the target obtained in Example 2 wassubject to sputtering in an oxygen-free Ar atmosphere. Although it waspossible to perform DC sputtering itself, problems arose in theproperties of the thin film Specifically, the refractive index of theobtained film decreased to 2.65, and the extinction coefficientincreased to 0.23. Accordingly, even if the target itself is free fromproblems, when it is subject to sputtering in an oxygen-free Aratmosphere, it is not possible to obtain a favorable thin film. As forComparative Example 1, the results of the target are shown in Table 1,and the composition and results of the thin film are shown in Table 2.As shown in the Tables, the film composition was Ti: 32.3 at %, Ag: 3.7at %, O: 64 at %, O/Ti: 1.98, and O/(2Ti+0.5Ag): 0.96.

Moreover, although several other tests were conducted, it was discoveredthat, in cases where the Ag content exceeds 1.5%, problems arise fromdecrease in the refractive index and increase in the extinctioncoefficient if sputtering is not performed in an argon gas atmospherecontaining 0.1 to 16% of oxygen. Accordingly, when using the sinteredsputtering target of the present invention, particularly when the Agcontent is 1.5% or more, it is preferable to perform sputtering in anargon gas atmosphere containing 0.1 to 16% of oxygen.

Comparative Example 2

As the raw material, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) was used. Specifically, inComparative Example 2, only TiO₂: 100 (at %) was used without addingsilver powder. 1 kg of this powder was filled in a carbon die andsubject to hot press. The hot press conditions were 950° C. and bearingsurface pressure of 250 kgf/cm². The obtained sintered compact wasmachined to prepare a target of φ 152 mm and 5 mmt Consequently, thedensity increased to 97%. Nevertheless, the obtained target had aspecific resistance exceeding 100 Ωcm. The results are also shown inTable 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas-2% O₂ gasatmosphere with a gas pressure of 0.5 Pa, a gas flow rate of 50 sccm,and a sputtering power of 500 to 1000 w. Nevertheless, since abnormaldischarge occurred during the DC sputtering and caused an unstablestate, DC sputtering was discontinued and deposition was performed onceagain by way of RF sputtering. The film composition was Ti: 33.2 at %,Ag: 0 at %, O: 66.8 at %, O/Ti: 2.01, and O/(2Ti+0.5Ag): 1.01. Asputtered film of 500 Å was formed on the glass substrate. Therefractive index and extinction coefficient of the sputtered film weremeasured. The refractive index and extinction coefficient were measuredwith an ellipsometer using a light wavelength of 405 nm. These resultsare also shown in Table 2. Consequently, the refractive index decreasedto 2.59, and the extinction coefficient was 0.004. Although there is noparticular problem with the extinction coefficient, the refractive indexdecreased, abnormal discharge occasionally occurred, and there was aproblem in that the stability of DC sputtering would deteriorateconsiderably.

Example 3

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 10 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=99.9:0.1 (at %) and mixed. 1kg of the mixed powder was mixed with a dry blender so that the silveris uniformly dispersed in the titanium oxide powder. Subsequently, themixed powder was filled in a carbon die and subject to hot press. Thehot press conditions were 920° C. and bearing surface pressure of 350kgf/cm². The obtained sintered compact was machined to prepare a targetof φ 152 mm and 5 mmt Consequently, a target having a density of 98% anda specific resistance of 10 Ωcm was obtained. The grain size of the Agphase in the target was 10 μm. No abnormal discharge occurred during thesputtering. The results are also shown in Table 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas atmosphere with agas pressure of 0.5 Pa, a gas flow rate of 50 sccm, and a sputteringpower of 500 to 1000 w. It was possible to perform DC sputtering withoutany problem, and it was confirmed that the target has conductivity. Thedeposition rate improved considerably to 1.7 Å/sec/kW. A sputtered filmof 500 Å was formed on the glass substrate. The film composition was Ti:33.3 at %, Ag: 0.04 at %, O: 66.66 at %, O/Ti: 2.00, and O/(2Ti+0.5Ag):1.00. Incidentally, the Ag composition was analyzed with SIMS. Therefractive index and extinction coefficient of the sputtered film weremeasured. The refractive index and extinction coefficient were measuredwith an ellipsometer using a light wavelength of 405 nm. These resultsare also shown in Table 2. Consequently, the refractive index increasedto 2.63, and the extinction coefficient was 0.01. Thus, it was possibleto form a favorable interference film or protective film for an opticalrecording medium.

Example 4

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 15 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=98:2 (at %) and mixed. 1 kg ofthe mixed powder was mixed with a dry blender so that the silver isuniformly dispersed in the titanium oxide powder. Subsequently, themixed powder was filled in a carbon die and subject to hot press. Thehot press conditions were 920° C. and bearing surface pressure of 350kgf/cm². The obtained sintered compact was machined to prepare a targetof φ 152 mm and 5 mmt. Consequently, a target having a density of 96%and a specific resistance of 6 μcm was obtained. The grain size of theAg phase in the target was 15 μm. No abnormal discharge occurred duringthe sputtering. The results are also shown in Table 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas-1% O₂ gasatmosphere with a gas pressure of 0.5 Pa, a gas flow rate of 50 sccm,and a sputtering power of 500 to 1000 w. It was possible to perform DCsputtering without any problem, and it was confirmed that the target hasconductivity. A sputtered film of 500 Å was formed on the glasssubstrate. The film composition was Ti: 32.2 at %, Ag: 1.4 at %, O: 66.4at %, O/Ti: 2.06, and O/(2Ti+0.5Ag): 1.02. The refractive index andextinction coefficient of the sputtered film were measured. Therefractive index and extinction coefficient were measured with anellipsometer using a light wavelength of 405 nm. These results are alsoshown in Table 2. Consequently, the refractive index increased to 2.67,and the extinction coefficient considerably decreased to 0.006. Thus, itwas possible to form a favorable interference film or protective filmfor an optical recording medium.

Comparative Example 3

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 20 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=60:40 (at %) and mixed. 1 kgof the mixed powder was filled in a carbon die and subject to hot press.The hot press conditions were 950° C. and bearing surface pressure of250 kgf/cm². The obtained sintered compact was machined to prepare atarget of φ 152 mm and 5 mmt Consequently, the density increased to 90%.Nevertheless, the obtained target had a specific resistance of 0.0003Ωcm. The results are also shown in Table 1. The grain size of the Agphase in the target was 20 μm.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas-10% O₂ gasatmosphere with a gas pressure of 0.5 Pa, a gas flow rate of 50 sccm,and a sputtering power of 500 to 1000 w. The film composition was Ti:26.3 at %, Ag: 17.5 at %, O: 56.2 at %, O/Ti: 2.14, and O/(2Ti+0.5Ag):0.92. A sputtered film of 500 Å was formed on the glass substrate. Therefractive index and extinction coefficient of the sputtered film weremeasured. The refractive index and extinction coefficient were measuredwith an ellipsometer using a light wavelength of 405 nm. These resultsare also shown in Table 2. Consequently, the refractive index was 2.5and the extinction coefficient was 0.15. The extinction coefficientincreased and the refractive index decreased. However, abnormaldischarge did not occur. This is considered to be a result of theelectrical stability of the target due to a high Ag content regardlessof the grain size of Ag.

Example 5

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 20 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=90:10 (at %) and mixed. 1 kgof the mixed powder was mixed with a dry blender so that the silver isuniformly dispersed in the titanium oxide powder. Subsequently, themixed powder was filled in a carbon die and subject to hot press. Thehot press conditions were 920° C. and bearing surface pressure of 350kgf/cm². The obtained sintered compact was machined to prepare a targetof φ 152 mm and 5 mmt. Consequently, a target having a density of 95%and a specific resistance of 0.5 Ωcm was obtained. The grain size of theAg phase in the target was 5 μm. No abnormal discharge occurred duringthe sputtering. The results are also shown in Table 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas-2% O₂ gasatmosphere with a gas pressure of 0.5 Pa, a gas flow rate of 50 sccm,and a sputtering power of 500 to 1000 w. It was possible to perform DCsputtering without any problem, and it was confirmed that the target hasconductivity. A sputtered film of 500 Å was formed on the glasssubstrate. The film composition was Ti: 31.0 at %, Ag: 3.6 at %, O: 65.4at %, O/Ti: 2.11, 0/(2Ti+0.5Ag): 1.03. The refractive index andextinction coefficient of the sputtered film were measured. Therefractive index and extinction coefficient were measured with anellipsometer using a light wavelength of 405 nm. These results are alsoshown in Table 2. Consequently, the refractive index increased to 2.72,and the extinction coefficient considerably decreased to 0.008. Thus, itwas possible to form a favorable interference film or protective filmfor an optical recording medium.

Example 6

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 1 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=90:10 (at %) and mixed. 1 kgof the mixed powder was mixed with a dry blender so that the silver isuniformly dispersed in the titanium oxide powder. Subsequently, themixed powder was filled in a carbon die and subject to hot press. Thehot press conditions were 920° C. and bearing surface pressure of 350kgf/cm². The obtained sintered compact was machined to prepare a targetof φ 152 mm and 5 mmt. Consequently, a target having a density of 91%and a specific resistance of 0.6 Ωcm was obtained. The grain size of theAg phase in the target was 1 μm. No abnormal discharge occurred duringthe sputtering. The results are also shown in Table 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas-2% O₂ gasatmosphere with a gas pressure of 0.5 Pa, a gas flow rate of 50 sccm,and a sputtering power of 500 to 1000 w. It was possible to perform DCsputtering without any problem, and it was confirmed that the target hasconductivity. A sputtered film of 500 Å was formed on the glasssubstrate. The film composition was Ti: 31.4 at %, Ag: 3.5 at %, O: 65.1at %, O/Ti: 2.07, and O/(2Ti+0.5Ag): 1.01. The refractive index andextinction coefficient of the sputtered film were measured. Therefractive index and extinction coefficient were measured with anellipsometer using a light wavelength of 405 nm. These results are alsoshown in Table 2. Consequently, the refractive index increased to 2.74,and the extinction coefficient considerably decreased to 0.007. Thus, itwas possible to form a favorable interference film or protective filmfor an optical recording medium.

Comparative Example 4

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 50 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=90:10 (at %) and mixed. 1 kgof the mixed powder was mixed with a dry blender so that the silver isuniformly dispersed in the titanium oxide powder. Subsequently, themixed powder was filled in a carbon die and subject to hot press. Thehot press conditions were 920° C. and bearing surface pressure of 350kgf/cm². The obtained sintered compact was machined to prepare a targetof φ 152 mm and 5 mmt. Consequently, the obtained target had a densityof 97% and a specific resistance of 15 Ωcm. The grain size of the Agphase in the target was 50 μm. Subsequently, although an attempt wasmade to use the sputtering target produced as described above to form asputtered film on a glass substrate, abnormal discharge occurredfrequently during the sputtering and deposition was difficult. Thus, thedeposition was discontinued.

Comparative Example 5

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 10 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=90:10 (at %) and mixed. 1 kgof the mixed powder was mixed with a dry blender so that the silver isuniformly dispersed in the titanium oxide powder. Subsequently, themixed powder was filled in a carbon die and subject to hot press. Thehot press conditions were 920° C. and bearing surface pressure of 350kgf/cm². The obtained sintered compact was machined to prepare a targetof φ 152 mm and 5 mmt. Consequently, the obtained target had a densityof 96% and a specific resistance of 2 Ωcm. The grain size of the Agphase in the target was 10 μm. The results are also shown in Table 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas-20% O₂ gasatmosphere with a gas pressure of 0.5 Pa, a gas flow rate of 50 sccm,and a sputtering power of 500 to 1000 w. Although it was possible toperform DC sputtering without any problem, the deposition rate wasextremely slow at 0.3 Å/sec/kW, and it was at a level where practicalapplication would be difficult. A sputtered film of 500 Å was formed onthe glass substrate. The film composition was Ti: 30.7 at %, Ag: 3.1 at%, O: 66.2 at %, O/Ti: 2.16, and O/(2Ti+0.5Ag): 1.05. The refractiveindex and extinction coefficient of the sputtered film were measured.The refractive index and extinction coefficient were measured with anellipsometer using a light wavelength of 405 nm. These results are alsoshown in Table 2. Consequently, the refractive index decreased to 2.59and the extinction coefficient was 0.005.

Example 7

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 10 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=99:1 (at %) and mixed. 1 kg ofthe mixed powder was mixed with a dry blender so that the silver isuniformly dispersed in the titanium oxide powder. Subsequently, themixed powder was filled in a carbon die and subject to hot press. Thehot press conditions were 920° C. and bearing surface pressure of 350kgf/cm². The obtained sintered compact was machined to prepare a targetof φ 152 mm and 5 mmt Consequently, a target having a density of 98% anda specific resistance of 7 Ωcm was obtained. The grain size of the Agphase in the target was 15 μm. No abnormal discharge occurred during thesputtering. The results are also shown in Table 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas atmosphere with agas pressure of 0.5 Pa, a gas flow rate of 50 sccm, and a sputteringpower of 500 to 1000 w. It was possible to perform DC sputtering withoutany problem, and it was confirmed that the target has conductivity. Thedeposition rate improved considerably at 1.8 Å/sec/kW. Accordingly, itis evident that the deposition rate can be improved considerably byperforming DC sputtering to the target in the Ar gas atmosphere. Asputtered film of 500 Å was formed on the glass substrate. The filmcomposition was Ti: 33.1 at %, Ag: 0.7 at %, O: 66.2 at %, O/Ti: 2.00,and O/(2Ti+0.5Ag): 0.99. The refractive index and extinction coefficientof the sputtered film were measured. The refractive index and extinctioncoefficient were measured with an ellipsometer using a light wavelengthof 405 nm. These results are also shown in Table 2. Consequently, therefractive index increased to 2.67, and the extinction coefficient was0.02. Thus, it was possible to form a favorable interference film orprotective film for an optical recording medium.

Example 8

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 10 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 10 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=99.5:0.5 (at %) and mixed. 1kg of the mixed powder was mixed with a dry blender so that the silveris uniformly dispersed in the titanium oxide powder. Subsequently, themixed powder was filled in a carbon die and subject to hot press. Thehot press conditions were 920° C. and bearing surface pressure of 350kgf/cm². The obtained sintered compact was machined to prepare a targetof φ 152 mm and 5 mmt. Consequently, a target having a density of 98%and a specific resistance of 9 Ωcm was obtained. The grain size of theAg phase in the target was 10 μm. No abnormal discharge occurred duringthe sputtering. The results are also shown in Table 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas atmosphere with agas pressure of 0.5 Pa, a gas flow rate of 50 sccm, and a sputteringpower of 500 to 1000 w. It was possible to perform DC sputtering withoutany problem, and it was confirmed that the target has conductivity. Aswith Example 7, the deposition rate improved considerably at 1.8Å/sec/kW. Accordingly, it is evident that the deposition rate can beimproved considerably by performing DC sputtering to the target in theAr gas atmosphere. A sputtered film of 500 Å was formed on the glasssubstrate. The film composition was Ti: 33.3 at %, Ag: 0.2 at %, O: 66.5at %, O/Ti: 2.00, and O/(2Ti+0.5Ag): 1.00. The refractive index andextinction coefficient of the sputtered film were measured. Therefractive index and extinction coefficient were measured with anellipsometer using a light wavelength of 405 nm. These results are alsoshown in Table 2. Consequently, the refractive index increased to 2.66,and the extinction coefficient was 0.01. Thus, it was possible to form afavorable interference film or protective film for an optical recordingmedium.

Example 9

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 1 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 1.5 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=99.95:0.05 (at %) and mixed. 1kg of the mixed powder was mixed with a dry blender so that the silveris uniformly dispersed in the titanium oxide powder. Subsequently, themixed powder was filled in a carbon die and subject to hot press. Thehot press conditions were 920° C. and bearing surface pressure of 350kgf/cm². The obtained sintered compact was machined to prepare a targetof φ 152 mm and 5 mmt Consequently, a target having a density of 98% anda specific resistance of 10 Ωcm was obtained. The grain size of the Agphase in the target was 1.5 μm. No abnormal discharge occurred duringthe sputtering. The results are also shown in Table 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas atmosphere with agas pressure of 0.5 Pa, a gas flow rate of 50 sccm, and a sputteringpower of 500 to 1000 w. It was possible to perform DC sputtering withoutany problem, and it was confirmed that the target has conductivity. Thedeposition rate improved at 1.6 Å/sec/kW. Accordingly, it is evidentthat the deposition rate can be improved considerably by performing DCsputtering to the target in the Ar gas atmosphere. A sputtered film of500 Å was formed on the glass substrate. The film composition was Ti:33.3 at %, Ag: 0.02 at %, O: 66.68 at %, O/Ti: 2:00, and O/(2Ti+0.5Ag):1.00. The refractive index and extinction coefficient of the sputteredfilm were measured. The refractive index and extinction coefficient weremeasured with an ellipsometer using a light wavelength of 405 nm. Theseresults are also shown in Table 2. Consequently, the refractive indexincreased to 2.62 and the extinction coefficient was 0.007. Thus, it waspossible to form a favorable interference film or protective film for anoptical recording medium.

Example 10

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 1 μm and a purity of 4N (99.99%) and silver powder having an averagegrain size of 1.5 μm and a purity of 3N (99.9%) were used. These rawmaterials were blended to achieve TiO₂:Ag=99.99:0.01 (at %) and mixed. 1kg of the mixed powder was mixed with a dry blender so that the silveris uniformly dispersed in the titanium oxide powder. Subsequently, themixed powder was filled in a carbon die and subject to hot press. Thehot press conditions were 920° C. and bearing surface pressure of 350kgf/cm². The obtained sintered compact was machined to prepare a targetof φ 152 mm and 5 mmt. Consequently, a target having a density of 98%and a specific resistance of 10 Ωcm was obtained. The grain size of theAg phase in the target was 1.5 μm. No abnormal discharge occurred duringthe sputtering. The results are also shown in Table 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas atmosphere with agas pressure of 0.5 Pa, a gas flow rate of 50 sccm, and a sputteringpower of 500 to 1000 w. It was possible to perform DC sputtering withoutany problem, and it was confirmed that the target has conductivity. Thedeposition rate improved at 1.6 Å/sec/kW. Accordingly, it is evidentthat the deposition rate can be improved considerably by performing DCsputtering to the target in the Ar gas atmosphere. A sputtered film of500 Å was formed on the glass substrate. The film composition was Ti:33.3 at %, Ag: 0.005 at %, O: 66.695 at %, O/Ti: 2.00, andO/(2Ti+0.5Ag): 1.00. The refractive index and extinction coefficient ofthe sputtered film were measured. The refractive index and extinctioncoefficient were measured with an ellipsometer using a light wavelengthof 405 nm. These results are also shown in Table 2. Consequently, therefractive index increased to 2.61 and the extinction coefficient was0.005. Thus, it was possible to form a favorable interference film orprotective film for an optical recording medium.

Example 11

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 1 μm and a purity of 4N (99.99%), titanium powder having an averagegrain size of 15 μm and a purity of 3N, and silver powder having anaverage grain size of 1.5 μm and a purity of 3N (99.9%) were used. Theseraw materials were blended to achieve TiO_(1.9):Ag=99.95:0.05 (at %) andmixed. 1 kg of the mixed powder was mixed with a dry blender so that thesilver is uniformly dispersed in the titanium oxide powder.Subsequently, the mixed powder was filled in a carbon die and subject tohot press. The hot press conditions were 920° C. and bearing surfacepressure of 350 kgf/cm². The obtained sintered compact was machined toprepare a target of y 152 mm and 5 mmt. Consequently, a target having adensity of 98% and a specific resistance of 0.01 Ωcm was obtained. Thegrain size of the Ag phase in the target was 1.5 μm. No abnormaldischarge occurred during the sputtering. The results are also shown inTable 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar-4% O₂ gas atmospherewith a gas pressure of 0.5 Pa, a gas flow rate of 50 sccm, and asputtering power of 500 to 1000 w. It was possible to perform DCsputtering without any problem, and it was confirmed that the target hasconductivity. The deposition rate was 0.7 Å/sec/kW. A sputtered film of500 Å was formed on the glass substrate. The film composition was Ti:33.4 at %, Ag: 0.02 at %, O: 66.58 at %, O/Ti: 1.99, and O/(2Ti+0.5Ag):1.00. The refractive index and extinction coefficient of the sputteredfilm were measured. The refractive index and extinction coefficient weremeasured with an ellipsometer using a light wavelength of 405 nm. Theseresults are also shown in Table 2. Consequently, the refractive indexincreased to 2.61 and the extinction coefficient was 0.007. Thus, it waspossible to form a favorable interference film or protective film for anoptical recording medium.

Example 12

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 1 μm and a purity of 4N (99.99%), titanium powder having an averagegrain size of 15 μm and a purity of 3N, and silver powder having anaverage grain size of 1.5 μm and a purity of 3N (99.9%) were used. Theseraw materials were blended to achieve TiO_(1.5):Ag=99.99:0.01 (at %) andmixed. 1 kg of the mixed powder was mixed with a dry blender so that thesilver is uniformly dispersed in the titanium oxide powder.Subsequently, the mixed powder was filled in a carbon die and subject tohot press. The hot press conditions were 920° C. and bearing surfacepressure of 350 kgf/cm². The obtained sintered compact was machined toprepare a target of φ 152 mm and 5 mmt. Consequently, a target having adensity of 98% and a specific resistance of 0.008 Ωcm was obtained. Thegrain size of the Ag phase in the target was 1.5 μm. No abnormaldischarge occurred during the sputtering. The results are also shown inTable 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar-4% O₂ gas atmospherewith a gas pressure of 0.5 Pa, a gas flow rate of 50 sccm, and asputtering power of 500 to 1000 w. It was possible to perform DCsputtering without any problem, and it was confirmed that the target hasconductivity. The deposition rate was 0.6 Å/sec/kW. A sputtered film of500 Å was formed on the glass substrate. The film composition was Ti:33.4 at %, Ag: 0.006 at %, O: 66.594 at %, O/Ti: 1.99, andO/(2Ti+0.5Ag): 1.00. The refractive index and extinction coefficient ofthe sputtered film were measured. The refractive index and extinctioncoefficient were measured with an ellipsometer using a light wavelengthof 405 nm. These results are also shown in Table 2. Consequently, therefractive index increased to 2.60 and the extinction coefficient was0.01. Thus, it was possible to form a favorable interference film orprotective film for an optical recording medium.

Example 13

As the raw materials, titanium oxide (TiO₂) having an average grain sizeof 1 μm and a purity of 4N (99.99%), titanium powder having an averagegrain size of 15 μm and a purity of 3N, and silver powder having anaverage grain size of 5 μm and a purity of 3N (99.9%) were used. Theseraw materials were blended to achieve TiO_(1.95):Ag=99.9:0.1 (at %) andmixed. 1 kg of the mixed powder was mixed with a dry blender so that thesilver is uniformly dispersed in the titanium oxide powder.Subsequently, the mixed powder was filled in a carbon die and subject tohot press. The hot press conditions were 920° C. and bearing surfacepressure of 350 kgf/cm². The obtained sintered compact was machined toprepare a target of φ 152 mm and 5 mmt. Consequently, a target having adensity of 98% and a specific resistance of 0.08 Ωcm was obtained. Thegrain size of the Ag phase in the target was 5 μm. No abnormal dischargeoccurred during the sputtering. The results are also shown in Table 1.

Subsequently, the sputtering target produced as described above was usedto form a sputtered film on a glass substrate. As the sputteringconditions, DC sputtering was performed in an Ar gas atmosphere with agas pressure of 0.5 Pa, a gas flow rate of 50 sccm, and a sputteringpower of 500 to 1000 w. It was possible to perform DC sputtering withoutany problem, and it was confirmed that the target has conductivity. Thedeposition rate improved to 1.6 Å/sec/kW. Accordingly, it is evidentthat the deposition rate can be improved considerably by performing DCsputtering to the target in the Ar gas atmosphere. A sputtered film of500 Å was formed on the glass substrate. The film composition was Ti:33.8 at %, Ag: 0.04 at %, O: 66.16 at %, O/Ti: 1.96, and O/(2Ti+0.5Ag):0.98. The refractive index and extinction coefficient of the sputteredfilm were measured. The refractive index and extinction coefficient weremeasured with an ellipsometer using a light wavelength of 405 nm. Theseresults are also shown in Table 2. Consequently, the refractive indexincreased to 2.63 and the extinction coefficient was 0.09. Thus, it waspossible to form a favorable interference film or protective film for anoptical recording medium.

Comparative Example 6

In this Comparative Example, the target obtained in Example 11 wassubject to sputtering in an oxygen-free Ar atmosphere. Although it waspossible to perform DC sputtering itself, problems arose in theproperties of the thin film. Specifically, the refractive index of theobtained film decreased to 2.58, and the extinction coefficientincreased to 0.21. Accordingly, even if the target itself is free fromproblems, when it is subject to sputtering in an oxygen-free Aratmosphere, it is not possible to obtain a favorable thin film. As forComparative Example 6, the results of the target are shown in Table 1,and the composition and results of the thin film are shown in Table 2.As shown in the Tables, the film composition was Ti: 34.3 at %, Ag: 0.02at %, O: 65.68 at %, O/Ti: 1.91, and O/(2Ti+0.5Ag): 0.96.

Moreover, although several other tests were conducted, it was discoveredthat, in cases where the Ti content exceeds 34.0%, problems arise fromdecrease in the refractive index and increase in the extinctioncoefficient if sputtering is not performed in an argon gas atmospherecontaining 0.1 to 16% of oxygen. Accordingly, when using the sinteredsputtering target of the present invention, particularly when the Ticontent is 34.0% or more, it is preferable to perform sputtering in anargon gas atmosphere containing 0.1 to 16% of oxygen.

Comparative Example 7

In this Comparative Example, the target obtained in Example 12 wassubject to sputtering in an oxygen-free Ar atmosphere. Although it waspossible to perform DC sputtering itself, problems arose in theproperties of the thin film. Specifically, the refractive index of theobtained film decreased to 2.54, and the extinction coefficientincreased to 0.34. Accordingly, even if the target itself is free fromproblems, when it is subject to sputtering in an oxygen-free Aratmosphere, it is not possible to obtain a favorable thin film. As forComparative Example 7, the results of the target are shown in Table 1,and the composition and results of the thin film are shown in Table 2.As shown in the Tables, the film composition was Ti: 39.9 at %, Ag:0.006 at %, O: 60.094 at %, O/Ti: 1.51, and O/(2Ti+0.5Ag): 0.75.

Moreover, although several other tests were conducted, it was discoveredthat, in cases where the Ti content exceeds 34.0%, problems arise fromdecrease in the refractive index and increase in the extinctioncoefficient if sputtering is not performed in an argon gas atmospherecontaining 0.1 to 16% of oxygen. Accordingly, when using the sinteredsputtering target of the present invention, particularly when the Ticontent is 34.0% or more, it is preferable to perform sputtering in anargon gas atmosphere containing 0.1 to 16% of oxygen.

SUMMARY OF EXAMPLES AND COMPARATIVE EXAMPLES

The foregoing Examples and Comparative Examples illustratedrepresentative examples. Although not shown in the foregoing Examples,in cases where the composition of the thin film was 29.6 at % or moreand 34.0 at % or less of Ti, 0.003 at % or more and 7.4 at % or less ofAg, and oxygen as the remainder thereof, and O/(2Ti+0.5Ag) as a ratio ofoxygen to metals is 0.97 or more, and further where O/Ti as a ratio ofoxygen to Ti is 2 or more; all cases resulted in a high refractive indexand a low extinction coefficient as with foregoing Example 1 to Example7. Moreover, when the sputtering target contained the respectivecomponents at a composition ratio of (TiO_(2-m))_(1-n)Ag_(n) (provided 0m≦0.5, and 0.0001≦n≦0.2), and contained Ag particles having an averagegrain size of 15 μm or less; the specific resistance was 10 Ωcm or less,and favorable results were achieved in which no abnormal discharge wasobserved.

The present invention provides a thin film mainly comprising titaniumoxide having a high refractive index and a low extinction coefficient, asintered sputtering target mainly comprising titanium oxide suitable forproducing the thin film, and a method of producing a thin film mainlycomprising titanium oxide. The thin film obtained by the presentinvention can be used as films and layers for an optical informationrecording medium of electronic parts such as CDs and DVDs. In addition,the thin film of the present invention is particularly useful as aninterference film or a protective film for an optical informationrecording medium having superior transmittance and with minimaldeterioration in reflectance. Since a protective layer of high-meltingdielectrics must be durable against repeated thermal stress caused bythe heating and cooling, and must not allow such thermal effect toinfluence the reflective film or other areas, and since it is alsorequired to be thin and have low reflectivity and strength to preventalteration; the present invention is useful as such dielectricprotective layer. In addition, a material having the foregoingproperties can also be applied to architectural glass, automotive glass,CRTs and flat-panel displays; that is, such material can also be used asa heat reflective film, an antireflective film, and an interferencefilter.

We claim:
 1. A method of producing a thin film mainly comprisingtitanium oxide, comprising the step of sputtering a sintered sputteringtarget that comprises components of Ti, Ag and O, contains therespective components at a composition ratio of (TiO_(2-m))_(1-n)Ag_(n),where 0≦m≦0.5 and 0.0001≦n≦0.2, and has a specific resistance of 10 Ωcmor less, wherein said sputtering step is performed under an argon gasatmosphere without oxygen or with 0.1 to 16% of oxygen to form a thinfilm on a substrate such that the thin film contains 29.6 atomic percent(at %) or more and 34.0 at % or less of Ti, 0.003 at % or more and 7.4at % or less of Ag, and oxygen as the remainder thereof, and has a ratioof oxygen to metals, O/(2Ti+0.5Ag), of 0.97 or more.
 2. A method ofproducing a thin film mainly comprising titanium oxide according toclaim 1, wherein said sputtering is DC sputtering, and wherein, when anoxygen gas ratio used in the sputtering gas atmosphere is represented asb (%), the oxygen gas ratio is adjusted during said sputtering step tobe in a range of 0<b≦83.3n-0.17 when the composition ratio n of Ag inthe sputtering target is 0.0001≦n≦0.01.
 3. A method of producing a thinfilm mainly comprising titanium oxide according to claim 1, wherein saidsputtering is DC sputtering, and wherein, when an oxygen gas ratio usedin the sputtering gas atmosphere is represented as b (%), the oxygen gasratio is adjusted during said sputtering step to be in a range of17n-0.17≦b≦83n-0.17 when the composition ratio n of Ag is 0.01≦n≦0.2. 4.A method of producing a thin film mainly comprising titanium oxideaccording to claim 1, wherein said sputtering step is performed byadjusting an oxygen gas ratio (b) to b=0% when the composition ratio mis in a range of 0≦m≦0.05 and the composition ratio n of Ag is0.0001≦n≦0.01.
 5. A method of producing a thin film mainly comprisingtitanium oxide, comprising the step of sputtering a sputtering targetthat has a sintered structure, contains Ti, Ag and O as its constituentelements with a composition represented as (TiO_(2-m))_(1-n)Ag_(n) wherem and n are numerals satisfying 0≦m≦0.5 and 0.0001≦n≦0.2, has a specificresistance of 10 Ωcm or less, has a matrix phase of titanium oxide, andhas a Ag phase dispersed as particles within the matrix phase, whereinsaid sputtering step is performed under an argon gas atmosphere withoutoxygen or with 0.1 to 16% of oxygen to form a thin film on a substratesuch that the thin film contains 29.6 atomic percent (at %) or more and34.0 at % or less of Ti, 0.003 at % or more and 7.4 at % or less of Ag,and oxygen as the remainder thereof, and has a ratio of oxygen tometals, O/(2Ti+0.5Ag), of 0.97 or more.
 6. The method according to claim5, wherein the Ag phase particles existing in the sintered structure ofthe sputtering target have an average grain size of 15 μm or less.
 7. Athin film comprising titanium oxide produced by a process comprising thestep of sputtering a sintered sputtering target that comprisescomponents of Ti, Ag and O, contains the respective components at acomposition ratio of (TiO_(2-m))_(1-n)Ag_(n), where 0≦m≦0.5 and0.0001≦n≦0.2, and has a specific resistance of 10 Ωcm or less, whereinsaid sputtering step is performed under an argon gas atmosphere withoutoxygen or with 0.1 to 16% of oxygen to form the thin film on a substratesuch that the thin film contains 29.6 atomic percent (at %) or more and34.0 at % or less of Ti, 0.003 at % or more and 7.4 at % or less of Ag,and oxygen as the remainder thereof, and has a ratio of oxygen tometals, O/(2Ti+0.5Ag), of 0.97 or more.
 8. The thin film comprisingtitanium oxide according to claim 7, wherein the thin film has arefractive index in a wavelength region from 400 to 410 nm of 2.6 ormore and an extinction coefficient in a wavelength region from 400 to410 nm of 0.1 or less.
 9. The thin film comprising titanium oxideaccording to claim 8, wherein the thin film has a ratio of oxygen to Ti(O/Ti) of 2 or more.
 10. The thin film comprising titanium oxideaccording to claim 9, wherein the thin film has an extinctioncoefficient in a wavelength region from 400 to 410 nm of 0.03 or less.11. The thin film comprising titanium oxide according to claim 10,wherein the thin film is an interference film or a protective film. 12.The thin film comprising titanium oxide according to claim 11, whereinthe thin film forms part of an optical recording medium.
 13. The thinfilm comprising titanium oxide according to claim 7, wherein the thinfilm has a ratio of oxygen to Ti (O/Ti) of 2 or more.
 14. The thin filmcomprising titanium oxide according to claim 7, wherein the thin filmhas an extinction coefficient in a wavelength region from 400 to 410 nmof 0.03 or less.
 15. The thin film comprising titanium oxide accordingto claim 7, wherein the thin film is an interference film or aprotective film.
 16. The thin film comprising titanium oxide accordingto claim 7, wherein the thin film forms part of an optical recordingmedium.